The correct answer is option 4: manganese nodules.

Manganese nodules are mineral deposits that form on the ocean floor. They are composed mainly of manganese, but also contain other metals such as iron, nickel, cobalt, and copper. These nodules can range in size from small pebbles to large, potato-sized nodules.

Option 1: Calcium bearing minerals are not specifically associated with mineral deposits on the ocean floor. While calcium is present in seawater and can combine with other elements to form minerals, it is not a defining characteristic of ocean floor mineral deposits.

Option 2: Phosphorus bearing minerals are also not typically associated with mineral deposits on the ocean floor. While phosphorus is an essential nutrient for marine life and can be found in seawater, it is not commonly found as a major component of mineral deposits.

Option 3: Petroleum, or oil, is formed from the remains of ancient marine plants and animals. While petroleum can be found in the ocean floor in some areas, it is not generally considered a characteristic of mineral deposits.

In conclusion, the presence of manganese nodules is a key characteristic of mineral deposits on the ocean floor.